1. Field of the Invention
This invention relates generally to beam steering apparatus for a phased array antenna and more particularly to a flux driver circuit for supplying control pulses to respective magnetically controlled microwave phase shifters employed therein.
2. Description of the Prior Art
In electronically steered phased array antennas, a plurality of individual antenna radiating elements are normally arranged in a linear or matrix array to provide beam steering by electronic techniques. Beam steering is accomplished by altering the phase relation of signals on different radiating elements. This is done by changing the corresponding phase of the phase shift device in the phased array element. The phase shift devices normally include a ferrite rod located within a waveguide section which in turn is surrounded by magnetizing and demagnetizing coils. Pulses of proper durations are selectively applied to the coils so that the magnetic material in the phase shifter is first driven into saturation in one direction by a reset pulse, and then driven in the opposite direction with a variable pulse-width set pulse. The width of the set pulse is determined by the predetermined flux level to be established in the phase shifter.
In any phase array antenna system containing a matrix of phasers, it becomes desirable to multiplex the data applied to the phase shifters. A number of drivers time share a common data line, receiving data during the time the system is transmitting and receiving. The drivers accordingly store the phase data until it is needed for the ferrite phasers. After all the drivers have received their respective data, a load command triggers the drivers causing them to proceed through a switching sequence, of first resetting the flux to a reference remnant state and then setting the flux to a desired remnant state to provide the desired phase shift.
Each data signal is usually stored in a capacitor type device with a voltage proportional to the desired phase shift. This capacitor can either be a sample and hold circuit receiving a voltage amplitude or it can be part of an integrating circuit integrating at pulse length. After a selected storage time, a set pulse is produced with a length proportional to the capacitor voltage, or if flux feedback is used, the capacitor voltage is compared to the flux integral to terminate the pulse.
As the quantity of ferrite phasers is increased to achieve better radar performance, the antenna array becomes a densely packed piece of apparatus. Consequently, the size and power that may be alotted to each driver decreases requiring that the driver circuitry must be miniaturized, such as by monolithic techniques.
When attempting to miniaturize these driver circuits, several problems emerge; the capacitors used fail to have the necessary capacity, the leakage resistance in the circuits is too low, the circuit requires standby power and the resulting monolithic chip becomes extremely complex.